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SWIMMING MACHINES(黄金29篇第六篇) Tunas, mackerels, and billfishes (marlins, sailfishes, and swordfish) swim continuously.Feeding, courtship, reproduction, and even "rest" are carried out while in constant motion. As a result, practically every aspect of the body form and function of these swimming "machines" is adapted to enhance their ability to swim. three kind of fish's body is good for their ability to swim. Many of the adaptations of these fishes serve to reduce water resistance (drag). Interestingly enough, several of these hydrodynamic adaptations resemble features designed to improve the aerodynamics of high-speed aircraft. Though human engineers are new to the
game, tunas and their relatives evolved their "high-tech" designs long ago. human beings learn the feature of the fish into the high-speed aircraft. Tunas, mackerels, and billfishes have made streamlining into an art form. Their bodies are sleek and compact. The body shapes of tunas, in fact, are nearly ideal from an engineering point of view. Most species lack scales over most of the body, making it smooth and slippery.
The eyes lie flush with the body and do not protrude at all. They are also covered with a slick, transparent lid that reduces drag. The fins are stiff, smooth, and narrow, qualities that also help cut drag. When not in use, the fins are tucked into special grooves or depressions so that
they lie flush with the body and do not break up its smooth contours. Airplanes retract their landing gear while in flight for the same reason. describe how the features of the shape cut the drag. Tunas, mackerels, and billfishes have even more sophisticated adaptations than these to improve their hydrodynamics. The long bill of marlins, sailfishes, and swordfish probably helps them slip through the water. Many supersonic aircraft have a similar needle at the nose. aircraft learn the long bill of fish into increasing the speed. Most tunas and billfishes have a series of keels and finlets near the tail. Although most of their scales have been lost, tunas and mackerels retain a patch of coarse scales near the head called the corselet. The keels, finlets, and corselet help direct the flow of water over the body surface in such as way as to reduce resistance (see the figure). Again, supersonic jets have similar features. describe the tail of the plane also similar with fish. Because they are always swimming, tunas simply have to open their mouths and water is forced in and over their gills. Accordingly, they have lost most of the muscles that other fishes use to suck in water and push it past the gills. In fact, tunas must swim to breathe. They must
also keep swimming to keep from sinking, since most have largely or completely lost the swim bladder, the gas-filled sac that helps most other fish remain buoyant. describe how do the tunas breath. One potential problem is that opening the mouth to breathe detracts from the streamlining of these fishes and tends to slow them down. Some species of tuna have specialized grooves in their tongue. It is thought that these grooves help to channel water through the mouth and out the gill slits, thereby reducing water resistance. grooves help fish from being reduced by water resistance when they open mouth to breath. There are adaptations that increase the amount of forward thrust as well as those that reduce drag. Again, these fishes are the envy of engineers. Their high, narrow tails with sweptback tips are almost perfectly adapted to provide propulsion with the least possible effort.
Perhaps most important of all to these and other fast swimmers is their ability to sense and make use of swirls and eddies (circular currents) in the water. They can glide past eddies that would slow them down and then gain extra thrust by "pushing off" the eddies. Scientists and
engineers are beginning to study this ability of fishes in the hope of designing more efficient propulsion systems for ships. fish use their tail push off the eddies and scientists learn how to use it into ship. The muscles of these fishes and the mechanism that maintains a warm body temperature are also highly efficient. A bluefin tuna in water of 7°C (45°F) can maintain a core temperature of over 25°C (7 7"F). This warm body temperature may help not only the muscles to work
better, but also the brain and the eyes. The billfishes have gone one step further. They have evolved special "heaters" of modified muscle tissue that warm the eyes and brain, maintaining peak performance of these critical organs. fish maintain a core temperature to warm the eyes and brains working effeicently. | 
楼主: taoyukun-daidai
发表于 2009-8-6 22:41:22
发表于 2009-8-9 09:39:22
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